The present invention relates to a rotary shaft holding mechanism for a rotary variable element, and more particularly to a rotary shaft holding mechanism for effectively holding a rotary shaft of such devices as a variable capacitor element used in electronic devices such as various kinds of tuners and RF modulators, etc.
In order to reduce the size of electronic components such as tuners, it is necessary to reduce the size of the component parts. Efforts have been made to reduce the size of the support assemblies for movable portions of variable capacitors for tuners or the like, and a typical example of a conventional rotary shaft holding mechanism for a rotary variable element will be explained by referring to FIGS. 1 to 3. FIG. 1 is a cross section of the conventional rotary shaft holding mechanism for a rotary variable capacitor wherein a local oscillator 1 of RF modulator including a variable capacitor is received in a casing 2. FIG. 2 is a perspective view of the rotary shaft holding mechanism shown in FIG. 1.
In this example, a frame 3 of the local oscillator 1 receives fixed capacitors 4A, 4B, a variable capacitor 5, and a stripline 6 for defining an oscillation frequency. The oscillation frequency of the local oscillator 1 may be varied by adjusting the value of capacitance of the variable capacitor 5. The variable capacitor 5 is composed of a rotor section 5A rotatably supported by a rotary shaft 5C, and a stator section 5B. The rotary shaft 5C is rotatably supported by the frame with opposite end portions of the rotary shaft 5C being urged into corner portions 3C and 3D of large holes 3A and 3B formed in the side walls of the frame by elongate bias springs 7 and 8 fixedly disposed at respective corner portions 3C and 3D. Thus, the rotary shaft 5C is rotatably mounted to the frame 3 by a biasing force applied by the bias springs 7 and 8. A stopping plate 9 of an arc-like configuration is mounted to one end of the rotary shaft 5C so as to rotate therewith and define with a stopper plate 10 fixed to the flame 3 a mechanism for limiting the angle of rotation of the shaft 5C.
The capacitance value varied by inserting the tip of a screw driver into the slot formed at one end of the shaft 5C. Inadvertently, however, the tip of the screw driver may tilt the shaft 5C as shown in FIG. 3, and the rotor section 5A and the stator section 5B are likely to become shorted. Thus, in some electronic devices such as RF modulators, a power circuit thereof may be undesirably damaged by the short-circuit between the rotary and stator section.